The present invention utilizes the principles of Particle Jetting Technology (PJT), computer aided design (CAD), and Electrorheological Fluid (ER) technology to manufacture an article to a predetermined configuration.
The PJT process involves using computer controlled independently targeted particles to construct three dimensional structures whereas, traditionally, a physical article was manually constructed by individuals working from drawings of a 3D image. In the PJT process, particles are deposited onto a substrate in much the same manner that an ink jet printer produces two dimensional images. A structure would be produced by printing multiple cross sections with cold welding or rapid solidification providing cohesion between particles. This manufacturing system can automatically produce parts in a single step which would require multiple manufacturing stages using conventional techniques.
In one embodiment of the PJT principle, an ink jet mechanism (well known in that art) ejects a molten wax through a small orifice as a result of an impulse from a piezoelectric ceramic device. The ink jet mechanism is positioned by a three axis robot using conventional (CAD) software. The melt temperature of the wax and the distance from the ink jet orifice to the substrate may be adjusted such that cold welding or rapid solidification provides cohesion between the particle and the substrate. An ink jet mechanism was preferred for this embodiment because of its ability to control the production of individual particles, and because it provides sufficient initial velocity to eliminate the need for subsequent acceleration and the wax is a safe and versatile material.
The PJT process is adaptable to many curable or solidifiable materials such as waxes, UV curable polymers, thermoplastic materials, thermosetting materials, ceramics and metals. Of all the usable material, metals contain the most potential for industrial applications. PJT with metals enables the user to produce extremely dense, microcrystalline structures with plasma deposition.
One example of particle jetting technology is disclosed in an article entitled "3D Prototypes Shot From A Nozzle" in the Jun. 21, 1990 issue of Machine Digest.
An additional example of particle jetting technology is disclosed in an article entitled "Rapid Prototyping Shapes Up As A Low Cost Modeling Alternative" in the August 1990 issue of Modern Plastics.
Computer aided design (CAD) systems are known and allows an operator to operate a computer to design a three dimensional object and display the design on a screen or on paper.
It has also been known to control a mechanical operation or manufacturing process by a computer such as in robotics. For example, as set forth in U.S. Pat. No. 4,665,492 (column 1, lines 27-31) the milling of metal parts to produce a simple article by means of a computer aided milling machine has been widely applied. One such computer aided milling machine is that manufactured by the Cincinnati Milicros Company.
Electrorheological fluid technology is also known. Such fluids are suspensories of fine polarizable particles in a dielectric medium, typically oils. The particles can be polymers, ceramics, silicon or other materials as long as the particles meet specific or semiconductive properties. The ER fluids solidify as fast as 0.001 sec. to 0.0001 sec. when placed in an electric field and liquify completely once the electric field is removed. These materials have to date been used principally in the automotive industry as variable drive transmissions, variable hydraulic shock absorbers, and as rotational seals in high speed, high vacuum drivers.
In using the CAD software, as set forth in U.S. Pat. Nos. 4,665,492, and 5,134,569 issued respectively on May 12, 1987 and Jul. 28, 1992 to William E. Masters, (both incorporated herein by reference), a three dimensional object is described. The software then takes the completed object, and sections it into discrete layers having a predetermined thickness which is approximately equal to the size of the material droplets ejected from an ejection head of a particle jetting apparatus. The software then directs the robotic drive to position the ejection head at the coordinates where the first drop of material, for the first layer of the object (article) is to be deposited.
Once the computer has directed the robotic positioner to the correct X, Y coordinates, an ink-jet printer deposits the first drop of material and the robotic drive then proceeds to next set of coordinates and deposits another drop of material. This movement-deposition process continues until the first layer of the structure is completed. The computer then begins the deposition process for the next layer of the structure. Each layer is sequentially deposited on the previous layer until the 3D object is completed.
The problem with PJT occurs when trying to build an overhang structure. An overhang is that part of the structure that is attached to, rather that built upon, an underlying part of the structure. As an example, consider the PJT fabrication of a simple "T"-structure. The vertical member of the T is easily fabricated, depositing one layer of the structure sequentially upon the previous layer. However, the horizontal cross-member of the "T" requires a support structure upon which the particles must be deposited and unfortunately, during the PJT process, described supra, the particles would adhere to the support structure.
Ideally, what is desired is a support material that would act as a surrogate surface during the deposition of an overhand structure, or the like, that could easily be removed when the article was completed. Because of their ability to rapidly change from a fluid to a solid and then back to a fluid, electrorheological fluids are suitable as support materials.
Prior to the present invention, the state of the art of support materials relied on differences in intrinsic properties such as melting point or physical properties such as solubility between the build and support material. Typically, a wax with a lower melting point than the build material would be used. The support wax would be deposited in a similar manner as the build material. Then once the part was completed, it would be heated to remove the support material. In the case of different polymers, the part would be placed into a solvent that preferentially dissolved the support material.
The obvious disadvantages to this process are that the melting of the support material would be incomplete for that the build material would soften during the heat cycle. The same would be true with the dissolution process. The solvent would leave traces of material on the part, and possibly soften the build material. The use of electrorheological fluids overcomes these advantages and by changing its viscosity it can serve as a support material that is cheap, easy to handle. The material will lend support as long as an electric field is applied, and is removed by simply removing the electric field. Furthermore, when the ER support material is in a fluid state, it is easily pumped into and out of the building chamber. A further advantage of using ER material as support material is that it can be deposited from the ink jet and if a structure requires fabrication of a complex overhang, the ER fluid can be deposited from the ink-jet printer head into small spatial areas. Thus the size of the support structure is easily tailored.
Electrorheological fluid technology is disclosed in the following U.S. Pat. Nos.: 4,033,892, issued Jul. 5, 1977; 4,687,589, issued Aug. 18, 1987; 4,744,914, issued May 17, 1988; 2,417,850 issued Mar. 25, 1947; 2,661,596, issued Dec. 8, 1953; 3,047,507, issued Jul. 31, 1962; 3,970,573 issued Jul. 20, 1976; 3,984,449, issued Oct. 5, 1976; 4,033,892, issued Jul. 5, 1977; 4,129,513, issued Dec. 12, 1978; 4,687,589, issued Aug. 18, 1987; and 4,733,914, issued May 17, 1988.
It is therefore an object of the present invention to provide a process and apparatus for producing a three-dimensional object automatically in response to the computer aided design of the object wherein the object, or portion thereof, is built up on a support structure formed of a material capable of changing state.
It is a further object of the present invention to form such support structure of electrorheological fluids.